1. Field of the Invention
The present invention relates to the use of acoustic microscopes for non-destructive valuation and, more particularly, to identifying molding compounds using an acoustic microscope.
2. State of the Art
Integrated circuit packages (i.e., chip packages or IC packages) normally comprise integrated circuit devices encapsulated with molding compounds comprised of resin and silica. There are several standard molding compounds used for integrated circuit packages. The characteristics of each of the molding compounds depends on the viscosity of the resin used and the amount of silica used in the formulation. After the integrated circuits have been encapsulated they usually are tested for de-laminations at the internal interfaces, voids in the molding compound, shifts in electrical parameters, broken bond wires, cracks, and so forth.
Conventional testing of integrated circuit packages is performed by either X-ray radiography or destructive cross-sectioning, but the acoustic microscope has been used as well. There are essentially three intrinsically different types of acoustic microscopes. The first is a scanning laser acoustic microscope which introduces a continuous plane wave of ultrasound on one side of the integrated circuit package with a piezoelectric transducer and detects the transmitted ultrasound on the opposite side with a rapidly scanning laser beam. The other two acoustic microscopes are reflection mode instruments known as scanning acoustic microscopes and C-mode scanning acoustic microscopes. Each of these acoustic microscopes uses a pulse-echo transducer that is focused at or below one of the surfaces of the integrated circuit package. The transducer is scanned across the integrated circuit package in raster fashion to create an image. Typically, the scanning acoustic microscope is used for high resolution images of the surface and near surface (typically less than 25 microns (0.001 inches) deep) of the integrated circuit package. The C-mode scanning acoustic microscope can penetrate into the integrated circuit package and is ideal for probing a specific level within the package. The acoustic microscope produces a color-mapped image of the integrated circuit package based on the density of the package, the lower the amount of reflected sound, the lower the density of the package and thus greater the amount of delamination.
Conventionally, acoustic microscopy is a tool that permits integrated circuit packages to be nondestructively analyzed for the occurrence of package voids, cracking and delamination. An acoustic microscope can detect changes in density that would indicate that a package defect such as delamination occurred at a certain portion of the object under analysis. The extent of delamination can be determined by interpreting color maps generated by data processed from sound waves reflected off the device under analysis.